Hogout machining generally refers to a process of forming a structural member by removing excess material from a piece of stock material, such as a plate or block, to arrive at the desired configuration and dimensions for the member. Oftentimes when practicing hogout machining, the dimensions and configuration of the structural member are such that appreciable amounts of material must be removed. Thus, while hogout machining provides a method for forming structural members having complex configurations, hogout machining can be costly due to the relatively large amount of excess material or scrap that typically must be removed and because the machining process can be time consuming and labor intensive. Hogout machining also can cause excessive wear on the cutting machine and tools, which can result in machine downtime and/or tool breakage that in turn can adversely affect the tolerances of the finished structural member. In addition, the availability of stock sizes of material limits the overall dimensions of a structural member formed by hogout machining.
In order to reduce material waste and machining times, other methods are used for forming the stock material to be used in machining a structural member. For example, one method is machined forging, which refers to the process of machining a part from a piece of forged stock material that approximates the final configuration. When machined forging is used, the amount of machining can be reduced because the forged stock material is first hand or die forged to dimensions that more closely approximate the desired dimensions of the finished member. However, the production of forged stock material can be time consuming and labor intensive and, in the case of die forgings, can require the production of costly forging dies. Die forgings can require ultrasonic inspection, as the forging process can cause internal cracks or other defects, especially when extreme deformation of the stock material is required. Additionally, both die and hand forging can cause residual stresses in the forged stock material that can remain in the finished structural member. Residual stresses can necessitate slower cutting speeds when hogout machining and can adversely affect the material properties and tolerances of the finished structural member.
Alternatively, a near-net shape can be formed by a variety of spraying processes in which particles are mixed with a gas and sprayed onto a surface of a substrate. For example, cold spraying generally refers to a process in which the particles and the gas are maintained at a temperature below the melting point of the particles. Cold spraying, which is further described in U.S. Pat. No. 5,302,414 to Alkhimov, et al. and U.S. Application No. 2002/0168466 A1 to Tapphorn, et al., can be used to deposit the particles onto the substrate to form a coating on the substrate. However, the deposition of the particles onto the substrate can be difficult to control, and certain detailed and/or complex configurations can be difficult to form by cold spraying. Further, the gas used for cold spraying can become trapped in the deposited material, thereby affecting the ductility or other properties of the material, as can occur, for example, if nitrogen is used to deposit titanium.
Thus, there remains a need for improved methods of forming stock material or “preforms” for use in forming machined structural members. Such preforms should approximate the desired dimensions and configuration of the structural member to reduce the machining time required during machining, as well as reduce waste material. The desired dimensions and configuration of the structural member should not be limited by the sizes of available stock materials. In addition, such preforms should have negligible residual stresses so that the finished machined member will have consistent material properties and dimensional tolerances.